1. Field of the Invention
The present invention is directed to a fuel system.
2. Description of the Related Art
A conventional fuel cell system is disclosed in, for example, Japanese Patent Laid-open Print No. Hei.8-293312 published without examination on Nov. 5, 1996. In this fuel cell system, upon start up and shut off, the fuel gas having a high concentration of CO and the fuel gas remaining in a reforming device are respectively temporarily fed to an evaporating part, instead of a fuel-cell stack at which water and the hydrocarbon family fuel are to be burned. Thus, the CO poisoning of a catalyst is avoided or suppressed.
However, upon start up of the foregoing conventional fuel cell system, the amount of water and hydrocarbon family fuel to be evaporated should be balanced with the burning amount in the evaporating part, which causes difficulty in control when the fuel cell system is started. In addition, when the fuel cell system is to be stopped, since the evaporating part is still in a burning operation, the cooling-down stage of the fuel cell system becomes longer and there is a fear of operating the reforming device when it is in its emptied state.
It is therefore an object of the present invention to provide a fuel cell system which is free from the foregoing drawbacks.
In order to attain a foregoing and other objects, the present invention provides a fuel cell system comprising a performing device for reforming a fuel such as a hydrocarbon or methanol to a fuel gas whose principal component is hydrogen; a fuel-cell stack for generating electricity by using the fuel gas and an oxidizing agent; a gauge for determining a concentration of CO in a fuel gas exhausted from the reforming device; a burner for burning the fuel gas, the burner being independent of the fuel-cell stack and the reforming device; and a switch for selecting supply of the fuel gas to either the fuel-cell stack or the burner.